First Battle of Fort Sumter

In 1860, South Carolina became the first state to secede from the United States. As more states followed suit and the Confederate States of America took shape, many federal installations in the South were taken over by state governments. Fort Sumter, in the harbor of Charleston, South Carolina, continued to fly the U.S. flag, even as Confederate forces surrounded it. Lincoln decided to resupply the fort but not reinforce it, unless resistance was met. After negotiations failed, the first shot was fired on April 12, 1861, in a bombardment that resulted in the fort's surrender. With that shot the Civil War began.

http://www.loc.gov/exhibits/treasures/trm117.html